A vapor-compression refrigerant cycle system (ejector cycle system) using an ejector as a refrigerant decompression unit and a refrigerant circulating unit is described in JP-B1-3322263 (corresponding to U.S. Pat. No. 6,574,987 and U.S. Pat. No. 6,477,857), for example. In this vapor-compression refrigerant cycle system, a first evaporator is arranged between the ejector and a gas-liquid separator located downstream from the ejector, and a second evaporator is arranged between a liquid refrigerant outlet side of the gas-liquid separator and a refrigerant suction port of the ejector, as an example.
The inventors of this application studied an example for switching a cooling function of the second evaporator. In this example, an electromagnetic valve is provided at an upstream portion of the second evaporator, and the electromagnetic valve is closed when the cooling function of the second evaporator stops. In this case, when the electromagnetic valve is closed, a refrigerant stream drawn from the second evaporator into the refrigerant suction port of the ejector is not generated. In this example, if the refrigerant suction port is opened at a lower portion of the ejector, lubrication oil (i.e., refrigerator oil) contained in a refrigerant flowing through the inside of the ejector falls into the refrigerant suction port by the weight of the lubrication oil. Accordingly, the lubrication oil stays in a refrigerant suction pipe connected to the refrigerant suction port of the ejector and the second evaporator, when the electromagnetic valve is closed. In this case, a returning amount of the lubrication oil returning to the compressor is reduced, and a lubrication oil shortage may be caused in the compressor.